Infrared detectors have been used to control lights and other electrical appliances. Such devices detect the change in the infrared radiation (heat) level within an area and activate the electrical appliance or sound an intrusion alarm. Typically, the change in heat results from a person entering or moving within the sensing area. The appliance remains turned on for a predetermined period of time after which, if no further change in the infrared level has occurred, the appliance goes off.
One problem encountered in certain types of these switches is that if the light or appliance is located within the sensing area, when the appliance is turned off, its cooling down may be detected and repeatedly triggers an activation cycle. It is not always practical to eliminate this problem by positioning the appliance outside the sensing area or by proper aiming of the detector.
Certain types of these infrared activated switches incorporate a visible light detector, so that the appliance is only activated if a person enters the room when the ambient light is below a given level. The given ambient light threshold level may be adjusted so that the switch activates the light only at night. In the past, the operator when setting that level, has not had any indication of when it is properly set, unless the heat pattern is also changing within the sensor area.